Curing an amine-treated chlorosulfonated polyethylene with sulfur and zinc oxide in the presence of a filler



STRESS (TENSILE STRENGTH) (PSI) Feb. 26, 1963 A. NERSASIAN 3,079,362

CURING AN AMINE-TREATED CHLOROSULFONATED POLYETHYLENE WITH SULFUR ANDZINC OXIDE IN THE PRESENCE OF A FILLER 0 Filed Aug. 15, 1958 3000 usomuha CHLOROSULFONATED POLYETHYLENE PIPERIDINATED cmonosuuonmo POLYETHYLENEl l I l 0 I00 200 300 000 500 000 STRAIN (ELONGATION 0%) .7 \INVENTORARTHUR NERlSAS/AN By/mmw ATTORNEY United States Patent Oflfice waistPatented Feb. 26, 1963 This invention is directed to elastomericchlorosulfonated polyethylenes, to the elastomeric products obtained byreacting them with secondary amines, and, to methods for curing suchaminated chlorosulfonated polyethylenes.

Valuable elastomers are made by chlorosulfonating normally solidpolyethylenes so as to contain 25 to 37% chlorine and 0.4 to 3.0%sulfur. These products, which contain the sulfur in the form of thechlorosulfonyl group, AO CI, are usually cured by means of magnesiumoxide or lead oxide (but not zinc oxide), along with an organic acidsuch as rosin, and, a rubber vulcanization accelerator. These elastomershave found wide acceptance because of their very good chemicalresistance (including ozone resistance and good weathering properties)and their very light color and good color stability. Recognizeddisadvantages which are sometimes significant, however, are the tendencyto scorch during compounding, the rather large proportion of lead oxidewhich must be used in some cases, the rather low tensile strength, and,the unusual character of the stress-strain relationship. Thisrelationship is different from that of most other elastomers in that itapproximately follows Hookes law. In other words, the elongation of atest sample of cured chlorosulfonated polyethylene is proportional tothe stress (usually expressed in pounds per square inch of originalcross section). On the other hand, as is well known, the stress requiredto produce a given increase in elongation for most natural and syntheticelastomers increases rapidly with elongation and then tends to decrease.Put another way, the conventional plot of elongation against stress(obtained for example with the machines which automatically recordstress-strain relationships) is substantially a straight line forchlorosulfonated polyethylene as represented by curve A in theaccompanying drawing; and, for typical elastomers is S-shaped asrepresented by curve B. Although this unusual stressstrain relationshipin chlorosulfonated polyethylene may be definitely advantageous in somerespects, it is obvious that it would be desirable to have achlorosulfonated product with the stress-strain propertiescharacteristic of the commonly used elastomers.

It is, therefore, an object of the present invention to.

furnish a cured polyethylene derivative having the desirable propertiesof chlorosulfonated polyethylene. It is a further object of the presentinvention to provide a cured polyethylene derivative having improvedtensile strength and the stress-strain relationship characteristic ofother elastomers. It is still a further object of the present inventionto obtain a cured polyethylene product, without the use of largeproportions of lead compounds and without significant risk of scorchingduring the compounding of said polyethylene product.

These and other objects will become apparent in the followingdescription and claims.

More specifically, the present invention is directed to a cured,elastomeric polyethylene derivative of improved physical propertiesobtained by reacting a chlorosulfonated polyethylene containing l45%chlorine and 0.5 to sulfur with dimethylamine, piperidine, morpholine,or pyrrolidine, followed by compounding the resulting sulfonamide with10-60 parts of a reinforcing agent, and conventional ingredients usedfor curing rubber with sulfur, including zinc oxide, and subjecting saidcompounded sulfonamide to conventional curing procedures.

Representative examples illustrating the present invention are asfollows; in these examples, the amides were made from chlorosulfonatedpolyethylene and isolated as shown in the following examples. Theproducts were then compounded, cured, and tested as shown in the tables.

EXAMPLE 1 The starting material is a chlorosulfonated polyethylenecontaining 27% chlorine and 1.3% sulfur, made from a high-pressurepolyethylene of density 0.916 and melt index of 10. A solution of 200 g.of this in 1 liter of carbon tetrachloride is treated under nitrogen at25 C. with 7.2 g. of dimethylamine in 50 ml. of carbon tetrachloride,added slowly with stirring. This quantity of dimethylamine isapproximately two molecules per SO Cl group. After 1 hour, thetemperature is raised to 50 and the treatment continued for 1 hour. Theproduct is precipitated by adding isopropyl alcohol and then washed on arubber mill with cold water, then alcohol, and finally dried at 50 in avacuum oven. The product is a light colored, readily milled, elastomer,containing 0.50% N, 30.0% C1, and 1.10% S. The theoretical values basedon complete reaction of the amine with the sulfonyl chloride groups toform the dimethyl sulfonamide are 0.44, 27.9, and 1.03, respectively.

A. The elastomer is stablized by incorporating 1.5% of an epoxy resin,made by condensing epichlorhydrin with propane-2,2-bisphenol in a molarratio of 2:1.

13. The dimethylamino sulfonamide made as above up to the precipitationstep is isolated directly by evaporating the carbon tetrachloride fromthe reaction mass, by drum drying. It of course, contains thedimethylamine hydrochloride formed in the reaction The presence of thissalt increases the swelling in water of the cured stock and decreasesthe rate of vulcanization and the tendency to scorch.

C. The dimethylamine hydrochloride in the above reaction mass can alsobe removed by reacting it with an isocyanate such as phenyl isocyanate.In this case enough isocyanate is added to the carbon tetrachloridesolution to react with the hydrochloride according to the equation:

and the solution is refluxed for two hours with a current of nitrogenpassing through to remove the hydrogen chlo ride. The product isstabilized with 1.5 parts of the above epoxide resin and isolated bydrum drying.

D. Similarly, an epoxy resin may be used to react with the hydrochlorideas follows:

Mainly R-GH(OH)CHzCl MezNHaT and some RCHCHz-O MezNH RGH(OH) CHzNMez Thecarbon tetrachloride solution to which 10 parts of the above epoxy resinper parts of elastomer has been added is heated at 60 C. for two hours,and blown with nitrogen to remove the amine, and drum dried.

E. Another method for avoiding the presence of the amine hydrochloridein the final product is to carry out the reaction between the secondaryamine and the ch10: rosulfonated polyethylene in the presence of alphapinene,

using only one equivalent of the amine. The hydrogen chloride formedappears to reactwith the pinene and a product of low water absorption isobtained.

EXAMPLE 2 Chlorosulfonated polyethylene like that used in Example l wasreacted with 13.6 g. of piperidIne, using the procedure of Example 1except that the reaction was complete in min. at 25; The product wasprecipitated, washed, and dried as in Example 1.

EXAMPLE 3.

The .chlorosulfonated polyethylene was treated with 11.4 g. ofpyrrolidine as in Example 1 except that the reaction mass was heated for15 minutes at 50 C. after 1 hour at 25. The product wasisolated as inExample l.

The ela'stomers obtained in the above examples were compounded andtested, the compounding recipes and test results being given 'inTablesI, II, and III. Table I compares the elastomers with each other and withchlorosulfonated polyethylene. TablelI compares the product of Example 1isolated and purified in various ways. Table [II compares variouselastomer compounds made from the dimethyl sulfonamide of Example 1.

A 1".: The elastorners were compounded as in Table I and cured forminutes at 153 C.

Table III VARIOUSLY COMPOUNDED DIMETHYLSULFONAMIDE A B C D EDirnethylsulionamide of Chlorinated Polyethylene 100 100 100 CarbonBlack (EPC) 30 Reinforcing Silica:

(OabO--Sil) 30 a (Hi-$1233). 30 Zinc Oxide..." 7.5 Titanium DioxiDipentnmethyleue Th Tetrasulfide 7 7 Sulfur 2 ZineDimethyldithiocarbamate. 1 Biel'captobenzothiavolo 1 Tensile Strength,lbs.lin. 3, 220 2, 740 2, 560 3,070 3,270 Elongation at Break, percent350 400 450 340 300 Modulus, lbs/in};

The cure was for 30 minutes at 153 C.

All vulcanizates in the above tables containingamnate'd chlorosulfonatedpolyethyenes of the present invention show the excellent ozoneresistance, not breaking during exposure under tension for 200 hours inan atmosphere containing 100 parts of ozone per million.

The stress-strain relationship is shown in detail for the product ofExample 2 compounded and cured as in Table I, as curve C in the drawing,in comparison with ordi- Table I CURING OF CHLORINATED POLYETHYLEN ESULFONAMIDES Chlorosul- Ex. 1 Ex. 3 Ex. 4 fonated Amine ComponentDimethyl- Ex. 2 Morpho- Pyrrol- Poly- I amine Piperidine line idmeethylene Recipe 1 Tensile, lbs/ink 30 min 3, 220 2, 210 3, 080 2, 930 2,200-2, 700 60 min 2, 290 3, 110 3, 070 2, 930 Elongation at break, p ce$23 558 Mmiulus, 400 270 457 490 100% i 2 61 as 2 ggg 2 253 ,71 1,27 i300% 2, 280 2, 490 1, 74 Perm. Set, percent, 5 ii a Compression Set (22lira/ 0.), percent g3 g2 25 Scorch Time (Min. at 250 F.) for rise of:

5 points 16 25 9 17 2-3 10 points, 18 29 13 23 5-6 20 point 28 38 17 3411-13 1 7 parts of ZuO, 7.5 of dipentamethylene thiuram tetrasulfide, oithe amide. The cure was at 153 C. for the time indicated.

and 30 of carbon black (EPO) were used with This is the recipe used inTable II and Table III, A..

2 40 parts of-PbO, 0.75 of dipentamethylene thiuram tetrasulfide, 0.5 ofbenzothiazyl disulfide, 2.5 of hydrogenated rosin, and 30 of carbonblack, per 100 parts 01' ehlorosulionated polyethylene. The cure was for30 min.

Table II CURING OF VARIOUSLY TREATED DIMETHYL SULFONAMIDES Ex. I Ex. IA-(Water- (Water- Ex. 1B Ex. 10- Ex. 1D- Washed) washed) Drum Iso-cyanateEpoxy Unstabi- Stabilized Dried Treated Treated lized Tensile, lbsJinF-2, 910 3, 070 2, 100 2, 990 2, 210 Elongation perce 330 330 530 400 320Modulus, lbs ins;

100% 356 433 295 446 300% 2, 710 2, 770 2, 060 2, 080 SeorehTime (Min.at 250 F.) for rise of:

6 points... 7 V 8 13 11 35 10 points; 17 I 21 1a 20 points. 22' 30 16(mm a minimum of 16 26 18 28 Percent Vol. increasein H O 17. 7 27. 3 27.4 39. 7

nary chlorosulfonated polyethylene compounded and cured like the controlin Table 1 (curve A) and in comparison with well-cured neoprene (curveB). It will be seen that the chlorosulfonated polyethylene givessubstantially a straight line, that is, the stress is directlyproportional to the strain as required by Hookes law. On the other hand,neoprene, a typical elastomer, gives an S-shaped curve, which is convextoward the elongation (strain) ax-is over most of its length, or, inother Words, the ratio of stress to strain is not a constant butincreases rapidly with elongation until the highest elongations arereached, when it decreases somewhat. The product of Example 2,piperidinated chlorosulfonated polyethylene, gives a similar curve (C),very different from that given by the parent chlorosulfonatedpolyethylene (curve A). It will be seen by inspection of the tables thatthe other amidated chlorosulfonated polyethylenes also show the sametype of stress-strain relationship. Thus the modulus (stress) for 300%elongation (strain) is always much more than three times the modulus for100%, or, in other words, the stress-strain ratio increases rapidly withelongation, as in typical elastomers.

As starting material, any normally solid polyethylene may be used butpreferably it should have a molecular weight, as ordinarily determined,between 10,000 and 100,000. The chlorosulfonation may be carried out byanyof the'known---n1ethods,- mostof which are disclosed in US. Patent2,586.363. The chlorine content may be between and 45% and preferablybetween 25 and 40%. The sulfur content, measuring the number of SO Clgroups, may be between 0.5 and 10% and preferably between 1 and 3%.

The chlorine content of the chlorosulfonated polyethylene used to makethe sul-fonamides affects the proper ties of the final cured material inmuch the same way as it affects those of the chlorosulfonatedpolyethylene cured directly with metal oxides. That is, when thechlorine is too low, the vulcanizates tend to lack resilience, and whentoo high, tend to be too stifi. The sulfur content of the originalchlorosulfonated polyethylene controls the number of sulfonamide groupswhich in turn affects the curing of the product. Thus, chlorinatedpolyethylene itself, without sulfona-mide groups, cures veryincompletely, giving very poor recovery and resilience. When sulfonamidegroups corresponding to 0.5 to 1.0% sulfur are present, satisfactorycures are obtained, and, on further increase, progressively faster curesresult; when 10% is reached, the curing rate is too fast to beordinarily practical.

The reaction of chlorosulfonated polyethylenes with ammonia and aminesis discussed in U.S. Patent 2,615,000. The reaction is preferablycarried out in the presence of a solvent for the chlorosu-lfonatedpolyethylene, a very suitable solvent being the carbon tetrachloride, inwhich the chlorosulfonation of the polyethylene is usually carried out.Other chlorinated hydrocarbons are suitable and also oxygenated solventssuch as methylethyl ke-tone, methylisopropyl ketone and dioxane. Meansmust usually be provided for reacting with or otherwise removing thehydrogen chloride formed. A convenient way to do this is to use twicethe theoretical quantity of amine required to form the sulfonamide. Thereaction usually proceeds readily at temperatures between 0 and 100 C.Higher temperatures sometimes cause darkening. Example 1 gives severalalternative ways dealing with the hydrogen chloride formed in thereaction.

The vulcanization of the aminated chlo-rosulf-onated polyethylenes ofthe present invention is carried out with sulfur or with an agentfurnishing sulfur, as in the vulcanization of natural rubber, with theonly requirement, as explained above, that zinc oxide (3 to parts) and areinforcing agent (10 to 60 parts per 100 parts of the elastomer) mustbe present. The thiuram sulfides are a preferred class of accelerators.The conventional curing temperatures are satisfactory and the curingtimes required for good cures are within the range used for naturalrubber and similar elastomers. For an excellent discussion of rubbercompounding and curing, see Encyclopedia of Chemical Technology (Kirkand Othmer, New York, 1953), vol. 11, p. 892 et seq.

The present invention sets forth an unexpected discovery that certainsulfonamides of chlorinated polyethylene, are curable by means ofconventional rubber-curing agents; however, it is required that from 3to 30 parts zinc oxide and a reinforcing pigment be included to give(without scorching) vulcanizates having the described improvedproperties. In the past, it has been thought that the curing ofchlo-rosulfonated polyethylene and its derivatives could take place onlythrough the reaction of the sulfonyl chloride groups with divalent metaloxides or diamines, presumably with the formation of cross-links betweenthe polymer molecules, or through double bonds introduced into themolecule, for example by reacting the sulfonyl chloride groups withunsaturated amines, to form unsaturated sulfona-mides. However, it hasbeen found that unsaturation is necessary in the sulfonamides forcuring. Thus when N-ethyl allyl amine is used the resulting product(compounded with MgO, sulfur, mercaptobenzothiazole and benz thiazyldisulfide) cures well, becoming highly elastic. On the other hand, whenthe chlorosulfonated polyethylene is reacted with the isomeric butsaturated piperid-ine and the product, compounded and heated in the sameway, it undergoes some change, but does not give an elastic product, asis shown by compression set of compared with 9% for the unsaturatedsulfonarnide. Similarly, chlorosulfonated polyethylene itself, whencompounded and heated in the same way, does not give an elastic product.

It is therefore unexpected and contrary to all that was reviously knownabout such systems, that a completely saturated sulfonamide could becured to a truly elastic vulcanizate which moreover is superior to curedchlorosulfonated polyethylene in a number of ways. These advantages areobtained, however, only according to the present invention. Thus, otheroxides, such as MgO, PhD, and Fe O can not be substituted for ZnO andnon-rein forcing agents such as Ti0 and ZnO, give very poor cures in theabsence of reinforcing pigments. Similarly, the amides formed byreaction with secondary amines other than those of the present invention(and also with primary amines) give products which are deficient in oneor more of the properties in which the products of this invention areoutstanding.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that this invention is not limited to the specificembodiments thereof except as defined in the appended claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A cured polyethylene derivative prepared by reacting chlorosulfonatedpolyethylene containing 10 to 45% chlorine, and, 0.5 to 10% sulfur withan amine compound taken from the group consisting of dimethylamine,piperidine, morpholine and pyrrolidine, said amine being present in atleast the amount required to react with all of the chlorosulfo-nylgroups of said chlorosulfonated polyethylene, followed by mixing theresulting sulfonarnide with from 10 to 60 parts per 100 parts of saidsulfonamide of a rubber reinforcing agent selected from the groupconsisting of carbon black and silica and from 3 to 30 parts, per 100parts of amide elastomer, of zinc oxide, followed by compounding saidsulfonamide with sulfur and curing said compounded sulfonamide.

2. A cured polyethylene derivative prepared by reacting chlorosulfonatedpolyethylene containing 10 to 45% chlorine, and, 0.5 to 10% sulfur withdimethylamine,

said amine being present in at least the amount required to react withall of the chlorosulfonyl groups of said chlorosulfonated polyethylene,followed by mixing the resulting sulfonamide with from 10 to 60 partsper 100 parts of said sulfonamide of a rubber reinforcing agent selectedfrom the group consisting of carbon black and silica and from 3 to 30parts, per 100 parts of amide elastomer, of zinc oxide, followed bycompounding said sulfonamide with sulfur and curing said compoundedsulfonamide.

3. A cured polyethylene derivative preparedby reacting chlorosulfonatedpolyethylene containing 10 to 45% chlorine, and, 0.5 to 10% sulfur withpiperidine, said amine being present in at least the amount required toreact with all of the chlorosulfonyl groups of said chlorosulfonatedpolyethylene, followed by mixing the resulting sulfonamide with from 10to 60 parts per 100 parts of said sulfonamide of a rubber reinforcingagent selected from the group consisting of carbon black and silica andfrom 3 to 30 parts, per 100 parts of amide elastomer, of zinc oxide,followed by compounding said sulfonamide with sulfur and curing saidcompounded sulfona'mide'.

4. A cured polyethylene derivative prepared by reacting chlorosulfonatedpolyethylene containing 10 to 45% chlorine, and, 0.5 to 10% sulfur withmorpho1ine',said

amine being present in at least the amount required to react with all ofthe chlorosulfonyl groups of said chlorosulfonated polyethylene,followed by mixing the resulting sulfonamide with from 10 to 60 partsper 100 parts of said sulfonamide of a rubber reinforcing agent selectedfrom the group consisting of carbon black and silica and from 3 toparts, per 100 parts of amide elastomer, of zinc oxide, followed bycompounding said sulfonamide with sulfur and curing said compoundedsulfonamide.

5. A cured polyethylene derivative prepared by reacting chlorosulfonatedpolyethylene containing 10 to chlorine, and, 0.5 to 10% sulfur withpyrrolidine, said amine being present in atleast the amount required toreact with all of the chlorosulfonyl groups of said chlorosul fonatedpolyethylene, followed v by mixing the resulting sulfonaniide with from10 to parts per parts of said sulfon'amide of a rubber reinforcing agentselected from the group consisting of carbon black and silica and from 3to 30 parts, per 100 parts of amide elastomer, of zinc oxide, followedby compounding said sulfonamide with sulfur and curing said compoundedsulfonamide.

References Cited in the file of this patent UNITED STATES PATENTS2,615,000 Bradley Oct. 21,- 1952 2,646,422 Strain July 21, 19532,852,497 Thompson Sept. 16, 1958 2,879,261 Johnson Mar. 24; 1959FOREIGN PATENTS" V

1. A CURED POLYETHYLENE DERIVATIVE PREPARED BY REACTING CHLOROSULFONATEDPOLYETHYLENE CONTAINING 10 TO 45% CHLORINE, AND, 0.5 TO 10% SULFUR WITHAN AMINE COMPOUND TAKEN FROM THE GROUP CONSISTING OF DIMETHYLAMINE,PIPERIDINE, MORPHOLINE AND PYRROLIDINE, SAID AMINE BEING PRESENT IN ATLEAST THE AMOUNT REQUIRED TO REACT WITH ALL OF THE CHLOROSULFONYL GROUPSOF SAID CHLOROSULFONATED POLYETHYLENE, FOLLOWED BY MIXING THE RESULTINGSULFONAMIDE WITH FROM 10 TO 60 PARTS PER 100 PARTS OF SAID SULFONAMIDEOF A RUBBER REINFORCING AGENT SELECTED FROM THE GROUP CONSISTING OFCARBON BLACK AND SILICA AND FROM 3 TO 30 PARTS, PER 100 PARTS OF AMIDEELASTOMER, OF ZINC OXIDE, FOLLOWED BY COMPOUNDING SAID SULFONAMIDE WITHSULFUR AND CURING SAID COMPOUND SULFONAMIDE.